1. Field of the Invention
The present invention concerns a paint medium for applying overglaze to porcelain.
2. Description of the Prior Art
In the ceramic industry overglaze paint has hitherto been applied by means of a paint medium the main ingredients of which are fat oils and turpentine and which may further contain various organic solvents and other organic substances of undetermined composition, e.g. tar. These known paint media have substantial drawbacks, in part on account of an inconstant composition which is due to varying provenance of the turpentine, and in part on account of health risk and irritant smell. In later years attention to health risk has increased and now there are prescribed such minimum limits to the contents in the air of especially the constituents of turpentine that the traditional paint media can only be used if at the same time there is a substantial air displacement or adequate ventillation in the premises.
Consequently, there is a need for a paint medium which does not present any health risk and which is composed of well defined constituents so that constant properties may be imparted to it. However, the difficulties in providing such a medium are great as a consequence of the very special properties required from an overglaze paint and which are: that it shall adhere to the glaze, shall dry up quickly to a hard and lustrous film, must not give problems in evaporation and combustion of the constituents, which could result in peeling and crackle of the decoration of drying and burning, must not give rise to an ion reaction between colour and medium resulting in coagulation and lumping, must not foam, and otherwise should be of such nature that the decoration aids are easy to clean. Besides, a new paint medium should preferably have the same technical qualities as the known media on the basis of oil and organic solvents so that the painter has no problems in switching over from one medium to another. Among these qualities which are of special importance to the user are, for example, good moistening, the possibility of painting several times on top of existing paint, and the possibility of varying a brush stroke by taking up paint, i.e., paint removal.